I've just had this happen to me. One of my sims was in the middle of a hangout with another player-controlled sim (at level 3 of a relationship story). I sent my sims to a party (where I added 2 or 3 more sims to the contact lists of my sims). I reloaded the app after minimizing it and when I did the sim my sim was in a hangout with had vanished off the contact list of all my sims and the story had disappeared, but my sim was still in a hangout (however, there were no options to spend energy for that hangout and when the hangout completed, no relationship points were earned.
I've had this happen before, but not in quite a while and in the past I'd often suspected that this is somehow related to adding other sims at parties as contacts. This time made me very suspicious that this issue is somehow related to adding other sims as contacts because this is the first time that it happened where I had proof of roughly how long ago the sim in question was still in my contact list and the number of things I had done in between was quite limited.
